In some systems, such as therapeutic systems employed in the treatment of disease, a fluid is conveyed or delivered to a target, such as a cancerous tumor, through a conduit that includes a coupling. For a fluid that includes microparticles, such as radioactive microparticles or radioactive microspheres, the microparticles can become trapped at the coupling.
Some microparticles are trapped in gaps that result from mechanically mismatched components in the coupling. Other microparticles are trapped in regions of stagnant fluid flow, such as regions in which the fluid velocity is less than the saltation velocity. Corners and discontinuities in the coupling can create regions of fluid expansion in which the fluid velocity is less than the saltation velocity. A force field, such as gravity, can also contribute to the trapping of microparticles. In some systems, more than fifty percent of the microparticles in the flow become trapped. The trapped microparticles are not delivered to the target. For systems that attempt to solve this problem by conveying the fluid at high pressures, the risk of system leakage increases.
In a therapeutic system, to achieve effective treatment, substantially all microparticles introduced into the system should be delivered to the target. Failure to deliver substantially all microparticles to the target reduces the effectiveness of the treatment. Similarly, in a diagnostic system, to achieve an accurate diagnosis, substantially all microparticles introduced into the system should be delivered to the target. Further, for microparticles that constitute a medical device, under delivery of the microparticles to the intended target is an incident reportable to regulatory authorities.